Reducing Energy and Carbon Footprint at Fabs: A New Focus for SEMI Standards

Semiconductor tools fabs have always used a lot of energy. But for the last 40 years, increased process throughput and yield has always trumped any considerations of energy efficiency.

Not any more. Today, with global warming and the desire of many fab companies to be good corporate citizens, we’re seeing increased interest in saving energy and reducing carbon footprint. Never at the cost of reducing throughput, of course – the economics of the semiconductor industry will always make energy reduction a second-order priority (1). But even as a second-order priority, there are lots of opportunities. And SEMI Standards help.

If a fab wants to reduce its carbon footprint, and save energy, the obvious place to start is by reducing the energy used by tools and their support facilities, so that’s what we’ll concentrate on here.

But before we start, there are several other possibilities that might not be initially obvious.

How much energy is used in the fab, compared to the lifetime use of energy by the fab’s products? If the latter dominates, perhaps scarce engineering dollars should be focused on reducing chip energy consumption, not fab energy consumption. Both can be done, of course, and reducing fab energy consumption has more visible results. But it’s worth thinking about this question.

Energy obviously arrives at a fab in the form of electricity (mostly) and natural gas. But a significant amount of hidden energy also arrives embedded in raw process materials – gases, chemicals, wafers, etc. Might it be possible to reduce the energy content of these materials, before they are delivered?

In some cases, the carbon footprint of the employees’ cars, as they commute to and from work at the fab, forms a significant part of the fab’s carbon footprint. Are there simple ways to reduce this, such as ride-sharing programs, providing re-charging stations and preferred parking for electric vehicles, sponsored bus passes, and so forth?

How can we reduce tool power consumption? Four steps: measure it; provide energy information to process designers; adjust the recipes; and change future tool designs.

First, we need to understand that any tool consumes energy in two different ways. There’s the direct and obvious way: the tool is hooked up to electric power, and it uses that energy. Then there’s the indirect and less obvious way: the tool is hooked up to a variety of other utilities, such as process cooling water, clean dry air, vacuum, etc., each of which requires energy to produce. These two ways of consuming energy interact: for example, the more electric power a tool consumes, the more heat must be removed with PCW and fab air conditioning. So reducing the electric power consumption of a tool can have a multiplier effect by reducing the indirect power as well.

Second, we need to understand that tool energy consumption is influenced and controlled in part by the recipe design, and in part by the tool design.

SEMI E6 provides detailed instructions on measuring the electric power consumption of tools. The good news is that SEMI E6 electric power consumption reports are automatically generated by tool manufacturers during SEMI F47 voltage sag immunity testing, because the industry-standard test equipment for generating voltage sags also generates SEMI E6 reports. The bad news is that these SEMI E6 energy reports are highly recipe-dependent. Still, they provide useful information about how a tool consumes power in kilowatt-hours (kWh), on a per-wafer or a per-lot basis, during a standard recipe.

Provide energy information to process designers

Today, process designers receive, in most cases, absolutely no information about the energy consequences of their choices as they optimize their recipes. It’s time to change this.

For the indirect energy consumption, SEMI S23 provides useful conversion factors that inform process designers of the energy costs of all the important utilities: for example, de-ionized water at room temperature costs 9 kWh per cubic meter, and at 85ºC it costs 92 kWh per cubic meter, while the cooling load for the fab air conditioning is roughly 0.3 kWh for each kWh used by the tool. These conversion factors are especially useful because they are expressed in kilowatt-hours, allowing their results to be directly added to the direct energy consumption of the tool.

Adjust the recipes

There’s no guarantee, of course, that process designers will adjust their recipes to reduce energy consumption. But there is a guarantee that, without this information, they won’t.

Process designers properly concentrate their efforts on maximizing yield, throughput, and performance. But by providing them with energy information, we can, at a minimum, help expand this list to yield, throughput, performance, and energy efficiency.

In some cases we have investigated, the process designers were simply unaware of the energy costs of certain steps in the recipe. Once they became aware, they were willing to experiment in reducing these energy costs, especially in non-critical recipe steps.

And we have already seen a few cases in which simple, easily removed mistakes in a recipe that increased energy consumption, such as inadvertently turning on all the heaters in a tool while a wafer was being unloaded from a chamber, were quickly identified and fixed.

Change future tool designs

The biggest opportunity for energy reduction is found in the tool designs. But until recently, there has been very little reward for designing an energy efficient tool, so tool designers simply haven’t paid much attention to energy efficiency. There are huge opportunities for energy reduction.

But the only way these opportunities will get attention is if tool purchasers base their tool selection, in part, on energy efficiency, probably measured in kWh per wafer (2). By choosing a standard measure like this, tool purchasers can compare energy efficiency from different vendors, and reward vendors that provide energy efficient tools. (It’s important, when making this comparison, to specify a recipe, because the recipe has such a strong influence on energy consumption.)

The entire situation is analogous to energy consumption in automobiles. Once consumers started basing their vehicle selection, in part, on miles-per-gallon (mpg) rating, then automobile manufacturers started producing vehicles that get higher mpg. (The EPA specifies a standard driving cycle, equivalent to a standard recipe, for measuring mpg.)

Getting started

The place to start, right now, is with tool energy measurements. Using SEMI E6, it’s a simple process, especially if the tool is already running a specific recipe. Then use SEMI S23 to figure out the total tool energy, including all the indirect energy costs. That information alone will provide an excellent start to reducing fab energy consumption and carbon footprint.

Using SEMI E6, a tool’s power consumption data can be automatically recorded during SEMI F47 voltage sag immunity testing, using test equipment like Power Standards Lab’s Industrial Power Corruptor. This data can be seen in the next figure. Courtesy Power Standards Lab, www.PowerStandards.com

A tool’s power consumption is highly dependent on the recipe. Here we see the power consumption while a single wafer is processed. The different colors show different steps of the recipe, helping the recipe designer understand (and possibly reduce) the energy used during each step. Courtesy Power Standards Lab, www.PowerStandards.com

Alex McEachern (Alex@PowerStandards.com) is widely recognized as the world-wide authority on electric power at semiconductor fabs. He is the President of Power Standards Lab, which works with fabs and tool vendors throughout the world on electric power measurements.

Footnotes:

1. At some locations around the world, reducing energy consumption at fabs may become a first-order priority simply due to scarce energy. In the electric power industry, it takes a decade or two to build a new power plant, and several years to build a new substation. In the next decade or two, a fab that ought to be expanding may be limited by the availability of additional electric power, especially in island nations.

2. A different measure, kWh per cm2 of wafer, allows quick comparison for the same process on 200mm and 300mm wafers.